The present invention relates generally to an exposure apparatus, and more particularly to an exposure apparatus and method that scan-exposes a reticle pattern onto the plate. The present invention is suitable, for example, for an exposure apparatus and method that include a measuring system for measuring a position of a wafer surface. In the present invention, an object measured and focus-controlled (in other words, a target to be measured or a target to be controlled) is not limited to a plate to be exposed, such as a single crystal substrate of a semiconductor wafer and a glass plate for a liquid crystal display (“LCD”), and includes a reticle (mask) that has a circuit pattern.
A projection exposure apparatus has been conventionally been used to transfer a reticle pattern on a reticle onto a wafer via a projection optical system, and an exposure apparatus that accurately and economically exposes a wide screen at a high resolution has been increasingly demanded. A shorter wavelength of an exposure light and a higher numerical aperture (“NA”) of the projection optical system are effective to improve the resolution. A conventional stepper has been replaced mainly with a step-and-scan exposure apparatus (also referred to as a “scanner”) that relatively scans the reticle and the wafer through an exposure area of slit form to expand the exposure area.
Moreover, the scanner executes a focus leveling control (hereinafter, referred to as a “focus control” in this application) that sequentially accords the wafer surface with an optimal image plane for high quality exposure. The focus control obtains a position measurement result of a measurement point on the wafer surface before exposure, obtains position and tilt information based on the measurement result by a controller, and correctly drives a wafer stage that supports the wafer. The measurement information is obtained using a focus tilt measuring system that includes plural oblique incidence measuring systems. The measuring part includes a single type that pre-detects information of next exposure position while exposing and executes exposure and measurement in the same station, and a twin type that has a measurement station separated from an exposure station. The controller maintains, as a measurement offset, a difference between a measurement value of each point and the optimal image plane. See, for example, Japanese Patent Application, Publication No. 11-16827.
The shorter wavelength of the exposure light and the higher NA of the projection optical system decrease a focal depth and require strict accuracy (focus tilt accuracy) to accords the wafer surface with the optimal image plane. In addition, the number of measurement points has been decreased and a measurement offset accuracy has been deteriorated to improve the economy (throughput). Therefore, it is increasingly demanded to improve the measurement offset accuracy by few measurement points.
If a level difference by a transferred pattern etc. exists on the wafer surface, the measurement offset by a diffusion of a grazing incidence measurement light occurs according to a defocus amount in an optical axis direction. For example, if a level difference P extended in a perpendicular direction (Y direction) to an incident direction DI (X direction) of light from the measuring system exists on the wafer surface as shown in FIG. 4A, a signal that shows actual height after once greatly swinging is obtained from the level difference P as shown in FIG. 4B. This swing causes error measurement. Here, FIG. 4A is a schematic sectional view of a wafer surface 41 that has the level difference P. FIG. 4B is a waveform view of a position detected signal of the wafer surface 41.